مطالعه پدیده گرفتگی در شفاف‌سازی غشایی آب سیب به کمک سامانه غشایی سطح تراش

شفاف‌سازی آب میوه جهت بهبود خواص فیزیکوشیمیایی و بازارپسندی مهم است. به دلیل مصرف بالای انرژی، زمان‌بر بودن، تخریب ترکیبات حساس به حرارت و کاهش ارزش تغذیه ای در روش‌های سنتی، امروزه برای شفاف‌سازی آب میوه فرآیند‌های غشایی به کار گرفته شده است. یکی از مشکلات مهم فرآیندهای غشایی، کاهش شار تراوه ناشی از قطبش غلظتی و گرفتگی غشا می باشد. در این مطالعه، یک روش مکانیکی جدید برای ایجاد تلاطم در جریان به‌منظور کاهش اثرات نامطلوب قطبش غلظتی و گرفتگی غشا ایجاد شد. بدین منظور، از غشا اولترافیلتر با جنس پلی‌اتر سولفون (pes) و حد وزن مولکولی (mwco) 4 کیلو دالتون درون سامانه غشایی با تیغه‌های تراشنده سطح جهت شفاف‌سازی آب سیب استفاده شد. اثر پارامترهای عملیاتی شامل سرعت دوران تیغه ها (0، 600، 1400 و 2200 دور بر دقیقه)، فشار( 0.5، 1 و 1.5 بار)tmp، سرعت جریان(ffr) (10، 15 و 20 میلی لیتر بر ثانیه) و فاصله تیغه از سطح غشاء (2 و 5 میلی متر) بر فاکتور غلظت حجمی (vcf)، مقاومت گرفتگی، زمان وقوع هر کدام از مکانیسم‌های گرفتگی و مورفولوژی لایه کیک بررسی شد. طبق نتایج انجام فرایند در فشار 0.5، سرعت جریان 10 میلی‌لیتر بر ثانیه، سرعت دوران تیغه‌ها 600 دور بر دقیقه و فاصله 2 میلی‌متری تیغه‌ها از سطح غشا بهترین تاثیر را بر vcf و کاهش گرفتگی داشت. مکانسیم اصلی گرفتگی در فرآیند، تشکیل لایه کیک بود. چرخش تیغه‌ها شدت تشکیل لایه کیک و ضخامت آن بر سطح غشا را کاهش داده و منجر به افزایش سهم گرفتگی استاندارد شد. [1]- polyether sulfone[2]- molecular weight cut off[3]- trans membrane pressure[4]- feed flow rate[5]- volumetric concentration factor

evaluation of the fouling phenomenon during membrane clarification of apple juice using scraped surface membrane unit

introduction as a useful fruit for humans, apple (malus domestica) is a good sourceof antioxidants, minerals, ascorbic acid, vitamins, polyphenols, fibers and other essential elements with medicinal properties. improving the storage time of apple juice and maintaining the stability of extracts with high brix value (during transportation and storage) and its marketability by removing the remaining water as well as reducing the turbidity, viscosity and brown color caused by colloidal suspended solids. large (pectin, protopectin, pigments, polymeric carbohydrates, tannin, starch, cellulose, hemicellulose, fibers, etc.) is of great importance. due to the presence of colloidal suspended solid particles and compounds that settle over time (mold, bacteria, plant cell fragments, pectin-tannin complex), apple juice must be clarified before concentration. due to the high-energy consumption, time-consuming, degradation of thermo-sensitive components, and reduction of nutritional value in traditional methods, recently, the use of membrane concentration in food and beverage production holds great potential.. despite all the benefits of membrane processes, one of the critical problems is permeate flux decline due to the concentration polarization and membrane fouling. in this study, an innovative mechanical motion was developed to remove the cake deposits on the membrane surface towards mitigating adverse effects of polarization and fouling.materials and methodsmembrane scraped surface module was designed and made with polyethylene material. the membrane was enclosed between the lower and upper parts of the module. these two parts are connected with screws and create a cylindrical part. also, two caps are pressed axially to this cylindrical part by a metal frame to eliminate any unwanted leakage. the rotor shaft was coupled with an electric motor and the rotation of the output shaft was regulated by an inverter. a pump transferred the fresh fruit juice to the module through the inlet port and then it was divided into two output streams, permeate and retentate. the permeate was collected from the bottom of the module for further investigation and the retentate was returned to the juice tank. a polyethersulfone (pes) membrane with molecular weight cut-off (mwco) of 4 kda was used to clarify apple juice. effects of the blade rotation speed (0, 600, 1400 and 2200 rpm), transmembrane pressure (tmp) (0.5, 1 and 1.5 bar), feed flow rate (ffr) (10, 15 and 20 ml/s) and the distance of the blade from the membrane surface (2 and 5 mm) on volumetric concentration factor (vcf) and fouling phenomenon were evaluated. hermia model was used to study the main fouling mechanism and it was verified by scanning electron microscopy (sem) images.results and discussion  results showed that rotating the blade with speed of 600 rpm at tmp of 0.5 bar, ffr of 10 ml/s and 2 mm distance from the membrane surface had the best performance in vcf and reducing fouling. the main mechanism of fouling was cake formation. rotation of the blade decreases the intensity of cake formation and its thickness on the membrane surface and enhances the standard pore blocking. also increasing the blade rotation speed changes the main fouling mechanism to the standard pore blocking due to the cake disintegration on the membrane surface and the penetration of fine particles into the membrane pores.